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Exhaust throttle question K&B 7.5 inboard

Old 09-14-2003, 09:46 PM
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bosco777
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Default Exhaust throttle question K&B 7.5 inboard

I recently bought a used nitro deep vee off of E-bay. It is my fourth nitro vechicle, and my third nitro boat, so I am somewhere between experienced beginner to novice. Anyhow, this boat has a rear exhaust and a tuned pipe. However, it has been upgraded to an exhaust throttle. However, I know nothing about those. Whenever I try to start the engine, it will only idle if I keep my thumb over the carb, partially closing it off. I have tried adjusting the needle valve and what I assume to be the low speed mixture screw, but nothing seems to make a difference.

So here are my questions,
1. Any thoughts?
2. When you convert an engine to an exhaust throttle, do you remove the little carb piece that normally opens and closes?
3. If yes to number 2, does the low speed mixture valve become useless because the carb is essentialy "wide open"?
4. If I wanted to go back to a regular throttle assembly, what pieces would I need? I don't know what carb is on it now, but it has the needle valve connected directly to the carb rather than being remote.

If pictures would help, I can post some

thanks

Bosco
Old 09-15-2003, 04:59 PM
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Ron Olson
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Default RE: Exhaust throttle question K&B 7.5 inboard

I'll give it a shot. I don't have any experience with exhaust throttles and really don't want to. It seems to be a West Coast thing. The needle valve should be for high speed only. The butterfly or barrel in the exhaust controls the throttle. They are supposed to be more responsive to throttle changes but usually my boats run at or near wide open most of the time except when coming in to shore so this isn't an issue with me. Most of the conversions just have the carb removed then the needle installed where the carb screws went or probably in your case, a small venturi. To swap it back, you'll need a carb and exhaust manifold for it. If you still want to mees with what you have, make sure somehow that the exhaust throttle is cracked open a little then mess with the needle until it runs slightly rich then adjust from there.
Old 09-15-2003, 06:56 PM
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Lovinnitro
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Default RE: Exhaust throttle question K&B 7.5 inboard

All I know is the exhauast throttle on my K&B 7.5 ob was a pain in the but!!!!!!![:@]

Absolutely drove me nuts not being able to get even close to half throttle. I,m working on getting it straight now but had a couple o toys arrive in the last couple days!
Old 09-16-2003, 05:41 AM
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Doubledog
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Default RE: Exhaust throttle question K&B 7.5 inboard

LMAO,

Ron & LN [sm=lol.gif]

Hey, I've got a 3.5 w/exhaust throttle that will be getting wet hopefully in the next week or so and am a bit cautious of it also. But to be on the safe side, I've picked up a regular carb for next to nothing... $14 shipped. Not bad.

Post here or head over to Int'l Waters where I picked mine up at. Hope it works out for you.

http://www.intlwaters.com/yabbse/index.php?board=1
Old 09-16-2003, 03:12 PM
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Lovinnitro
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Default RE: Exhaust throttle question K&B 7.5 inboard

Hey There PHCM I hated my exhaust throttle on that 7.5 Even as Ron said about near WOT that's what I wish it was like all the time but everytime I even got CLOSE to half throttle.... BLEH.............(My motor dying sound) Hey guys check out the new post I got the new toy and an added suprise from my wife.

I gotta take some pics.. Peace

Also Bro, If your gonna switch over to a carby set up, don't forget you'll need an exhaust manifold. Cause if they are all the same that is where your existing butterfly is.
Old 09-16-2003, 04:17 PM
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Ron Olson
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Default RE: Exhaust throttle question K&B 7.5 inboard

If you have to or just to be cheap (like me), you could leave the exhaust throttle on and hook it up so that it is always wide open then put a carb on.
Old 05-17-2004, 10:15 PM
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bosco777
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Default RE: Exhaust throttle question K&B 7.5 inboard

Well, I have just about given up on using this motor with the exhaust throttle. In the past, I was able to get it to idle with my thumb over the ?carb?, but I can't even get it to do that now. It makes a pop, pop, pop sound, but it just doesn't seem to be turning over fast enough. I wonder if maybe the person I bought it from tried to modify the timing? I tried selling it on ebay for $175 (fiberglass deep vee, motor, and radio) but noone bid, so I guess I am finally going to fix it up.

Anyways, does anyone know what the best glow plug to use in a a very old K&B 7.5 inboard? Long or short?

Also, I have bid on a parts 7.5 motor on ebay [link=http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&category=34058&item=3193029616&rd=1]Parts Motor[/link]. I plan on using the exhuast manifold and carb from it. This motor looks just like my 7.5 (except for the flywheel).


Hopefully this will do the trick.

bosco
Old 05-18-2004, 01:55 PM
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woodbw
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Default RE: Exhaust throttle question K&B 7.5 inboard

Just finished four seasons using an exhaust throttle and I agree with all they are the worst item to add to an engine if you want to drop below 3/4 throttle. I have over the winter removed them from both my 3.5 and 7.5 and all that was required was a proper carb and an exhaust adapter. As Ron did my 3.5 the exhaust throttle is still on the boat just held wide open by a set screw I drilled into the side. Both boats have seen water this season and there is no decrease in performance noted yet I can now idle past to check out everything and power on after without loosing the engine.
Old 05-18-2004, 02:51 PM
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Square Nozzle
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Default RE: Exhaust throttle question K&B 7.5 inboard

I guess there are always two sides to a story. I have had Prather exhaust throttles on both my 3.5 rigger and my 7.5 rigger. Never had a bit of trouble with throttling or throttle response. Go figure!
Old 05-19-2004, 06:16 AM
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TERBObob
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Default RE: Exhaust throttle question K&B 7.5 inboard

Ok , myself , I have not had any experience with the conversions , but I will say that the old originals could not be beat . Not only did the rap out a LOT faster , but they also seemed like they had more power and Rpm's .
The only hard thing about a exhaust throttle was getting the carb and exhaust sync'ed together ( kinda like tuning in twin four barrels and a car , or worse , a six pack . ) Time consuming , but well worth it .
Without seeing your setup , I am taking a shot in the dark here . But would also be helpful viewing some pics of the motors carb and exhaust and linkage .
When you said about the needle , does it allow adjustment ? The way some of the older ones worked was that the carb still had the adjustments and the exhaust was kinda used as a built in tuned pipe ( if you will ) via the linkage from carb to exhaust butterfly/slider . ALthough I can not recall , nor did I own one for marine , the ones I am referring to were plane motors .
One more thing , what per cent fuel are you using and if possible , try a fuel that is 5 per cent higher than what you are using currently and also , if you can , try a hotter plug .
A LOT of folks overlook how important a glow is to a nitro . Most think that any will work ,( which is basically true ) , but , think of it as when you go and buy new plugs for your car . Very specific, huh ? Well , glows are not that sensitive or touchy , but there IS a LOT of variables there . I would try a hotter plug with a higher nitro before ditching the motor for a lost cause . ( 15 per cent minimum but , preferrably 20 )
The other thing , you mentioned that possibly the timing was messed with . Have you checked that as well ? A fellow CAN mess with the ports enough to were the engine will do as you say also - just pop off and not start . I am also assuming that your comp is good too .
Old 05-20-2004, 03:40 PM
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crrcboatz
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Default RE: Exhaust throttle question K&B 7.5 inboard

Put in a hotter plug, and play with the pipe setting. Exhaust throttles are sensitive to humidity and heat. If you get the pipe setting on they will make the motor accelarate far quicker that a carb. However you will probably never get it to idle like a carb motor. Give up something to get something!!!

Regards Curt

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